This invention relates to a passive safety device, especially an airbag system, for protecting the occupants of a vehicle, a land vehicle, rail vehicle or the like, from injuries during accidents, which is equipped with a sensor device or unit for detecting the vehicle accelerations and decelerations, an evaluating device or unit connected to the sensor device for evaluating the output signal of the sensor device, and a triggering device or unit connected to the evaluating device for the activation of an occupant protection system upon the reception of a trigger signal to protect the occupants from injuries. Furthermore, the invention concerns a method for triggering such a passive safety device. Finally, the invention also concerns optomechanical acceleration sensors for utilization, in particular, in a passive safety device of the above type and/or in a method for triggering such a safety device.
Passive restraints in automotive vehicles, airplanes and railroad vehicles, as well as methods for triggering such a safety device have been known. The airbag system in an automotive vehicle, for example, is such a passive restraint. In this safety system, upon the occurrence of a specific acceleration or deceleration, detected by a sensor device, the actual occupant safety unit is triggered; this being an airbag to be inflated within a specific predetermined time period. Passive restraints conventionally include the following functional or structural units: A sensor unit or means for detecting the vehicle acceleration and deceleration, an evaluating device unit or means connected to the sensor device for evaluation of the output signal of the sensor device, and a triggering unit or means connected to the evaluating unit for effecting activation of the (actual) occupant safety device to protect the occupants from injuries, upon the reception of a triggering signal. The above three units are sometimes mounted spatially separate in the corresponding vehicle. For example, in an automotive vehicle, the triggering unit is disposed together with the gas generator in the steering wheel or dashboard (glove compartment); whereas the evaluating unit together with the other electronic circuitry of the automotive vehicle is accommodated in a region readily accessible for the purpose of a simple exchange of individual modules, for example in the engine compartment. The sensor unit can be provided at a third location in the vehicle. All of these units are connected with one another by way of electrical cables the signal or data exchange among the individual units takes place electrically. A drawback in this arrangement resides in the susceptibility to failures inherent in the safety system on account of external electromagnetic interference pulses which can be coupled into the system via the electrical connecting lines and can bring about, in the most adverse case, an erroneous triggering of the occupant safety system. A weakening of the interference pulses can be obtained by complicated and expensive shielding measures, but such pulses cannot be prevented in every instance.
Furthermore, acceleration sensors are known in the art in a plurality of technical applications. Such acceleration sensors are utilized, inter alia, in the control of kinetic processes, or also as trigger elements for initiating certain processes upon the occurrence of accelerations higher than a predetermined threshold value. In the conventional acceleration sensors, an electrical switch is closed and/or opened (mechanical "spring acceleration sensor"), when a defined acceleration has been reached and/or exceeded, or alternatively, by the prevailing acceleration, an electrical signal is directly generated (acceleration sensor with piezocrystal). One disadvantage herein resides in that the sensor system is connected via electrical connecting lines herein to the total system into which the acceleration sensor is incorporated. Thereby, electromagnetic interference pulses can be coupled in, for example, which can lead to failures and, in the most adverse case, to an erroneous triggering.